This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

1. Solution Preparation
<ol>
	<li>Filter 60 g of ethyl lactate using a syringe and a 0.20 &#181;m syringe filter. Add 0.3 g of polyvinyl formal to the ethyl lactate. Place the solution into the oven at 50&#160;&#176;C for 4 hr. Shake the vial gently to see if the polymer has dissolved completely.
	<ol>
		<li>If the solution is cloudy or still shows optical inhomogeneities, return the vial to the oven for another 2 hr. This recipe is for a 0.5 wt% polymer solution, which is typically used for film thicknesses around 30 nm. Solutions with higher polymer weight content can be used for thicker films.</li>
	</ol>
	</li>
	<li>Prepare a PDAC solution by weighing 1.0 g of PDAC reagent in a 20 ml volumetric flask and filling the flask to the measuring line with deionized (DI) water. Swirl the solution gently before transferring it to a storage container.</li>
</ol>
2. Substrate Preparation
<ol>
	<li>CAUTION. Pour 60 ml of concentrated sulfuric acid into a clean 250 ml beaker. Slowly add 20 ml of 30% hydrogen peroxide. Wait until fuming subsides, then swirl the solution gently. The solution and the beaker will become very hot and the mixture is corrosive.</li>
	<li>Place a 150 mm Petri dish onto the hot plate and pour the acid into the dish. Set the hot plate to 100 &#176;C.
	<ol>
		<li>Place a 4&#39; silicon wafer into the acid with the polished side up. Gently push the wafer down in the middle with a pair of tweezers to make sure the entire surface is wetted. Leave the wafer in the acid for 30 min.</li>
	</ol>
	</li>
	<li>Remove the wafer from the acid with a pair of tweezers and rinse the front and back of the wafer thoroughly with DI water from a squirt bottle. The water should sheet off in a regular pattern. Dry the wafer in a clean bench.</li>
	<li>Rinse a disposable 3 ml syringe and a 0.2 &#181;m filter first with DI water and then with PDAC solution by drawing the liquid into the syringe, mounting the filter, and then pushing the liquid out through the filter.</li>
	<li>Mount a cleaned wafer in the spin coater. Draw up 1.0-1.2 ml of PDAC solution into the syringe and dispense it though the filter onto the middle of the wafer. Spin at 4,000 rpm for 15 sec, then transfer the wafer to a hot plate (preheated to 50 &#176;C) and let it sit for 30 sec.</li>
	<li>Rinse the dried PDAC layer off with DI water and let the wafer dry in the clean bench.</li>
</ol>
3. Film Fabrication
<ol>
	<li>Place a dry PDAC-treated wafer onto the spin coater.</li>
	<li>Rinse a disposable 3 ml syringe and a 0.45 &#181;m filter with the ethyl lactate solution using the procedure under 2.4).</li>
	<li>Deposit 2.5 ml of the ethyl lactate solution through the filter with the syringe in the middle of the wafer and spin for 10 sec at 200 rpm, then for 3 sec at 1,700 rpm (dependent on desired film thickness). There should be a uniform liquid film on the wafer.</li>
	<li>Let the film dry in the spin coater until it is visibly dry (typically 10-15 min), then place it on a hotplate (preheated to 50 &#176;C) for 10 min.</li>
	<li>Dice the films into smaller squares for liftoff, typically 2 cm x 2 cm, but can be larger, depending on the size of the film holder used (3.5.1-3.5.2). Alternatively, make two scribes for delaminating a wafer-sized film (3.5.3). 
	Note: Standard film holders are 19 x 19 mm, with a circular opening of 13 mm diameter in the middle. For wafer-sized films, use a wire hoop (e.g., stainless steel wire formed into a circle) with a diameter that is 1&#8221; smaller than the wafer. A circular opening is chosen because the films will typically absorb water during liftoff and swell. As the films dry on the holder, the water is removed and the film will shrink. A circular opening allows for an even distribution of stress.
	<ol>
		<li>Place the wafer on a cutting template. Use a square template on which all edges are taller than the wafer to prevent the straight edge used to guide the blade during scribing from touching the wafer. Mark the edges in 2 cm intervals to guide the placement of the straight edge during dicing. Push the wafer against two edges to align it.</li>
		<li>Place a straight edge along two alignment marks, and draw a razor blade gently along the straight edge to scribe the film. Apply enough pressure to mark the film, but not too much to mark the wafer itself and produce particles. On thicker films, the cutting line will be clearly visible.</li>
		<li>To liftoff a film in one piece from the wafer, scribe the wafer edge with a razor blade. Between the two flats on the wafer, scribe a strip wide enough to clamp the wafer onto the rack-and-pinion.</li>
	</ol>
	</li>
	<li>Fill a 190 x 100 mm culture dish with DI water. Clamp the wafer by the large flat to a rack-and-pinion mounted to a tilt stage and slowly lower it into the DI water. The film should separate from the wafer at the water line.
	<ol>
		<li>Continue lowering the wafer at a rate that gives the film enough time to separate from the wafer, rather than pushing the lift-off interface below the water line. When the first row of squares has detached from the wafer and is floating on the surface, pause the lowering of the wafer. For a wafer-sized film, continue immersing the wafer until the film detaches completely.</li>
		<li>Immerse the head of the film holder into the water and move it underneath the film. Line up the handle edge of the hoop with one of the film edges and touch the hoop with the film. If successful, the film will stick to the hoop.
		<ol>
			<li>For a wafer-size film, place the wire hoop underneath the scribed section, just a centimeter away from the edge. Make sure that the hoop is centered underneath the film before beginning the capture, maintaining some distance between film edge and hoop edge so that the film can wrap around the hoop and fold back on itself.</li>
		</ol>
		</li>
		<li>Retract the hoop slowly from the water at an angle of 35&#176;. Lift the film out of the water very slowly. 
		Note: For films less than 20 nm thick, increase the angle after about half of the film has been pulled from the water to almost 90&#176; (i.e., normal to the water surface) to avoid pulling the film through the holder. When changing the lift out angle, do so slowly to avoid pulling the film through the hoop.</li>
		<li>When the hoop is fully retracted, place it to the side to dry. Make sure the bottom of the hoop is free of drops before putting the hoop down, and use a curved surface (such as a wafer tray) to avoid creating a liquid seal between hoop and surface.</li>
		<li>If more scribed squares remain on the wafer, continue lowering the wafer into the water and repeat steps 3.6.1-3.6.4 above for remaining squares.</li>
		<li>Let the films dry O/N.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The PDAC substrate treatment is based on self-limiting electrostatic interactions, meaning substrates of any size can be easily treated provided that they are negatively charged (e.g., silicon or glass). Figures 1-2 shows very large thin films (up to 13 cm in diameter) fabricated using this protocol, with the only change being the volume of reagents used. The ultimate achievable size appears to be limited only by the deposition and delamination equipment or the ultimate strength of the polymer used to fabricate the free-standing structure. While the former is clearly a practical issue, the latter is not a simple reflection of the intrinsic strength of the polymer. We have found that evaporation rate during spin coating and solvent selection &#8212; among other factors &#8212; can determine the film strength (data not shown). The critical step in producing defect-free films over large areas is the liftoff procedure described in 3.5-3.6 in the procedure and shown in the video. Careful delamination of the thin polymer film ensures that tears or holes do not form in the final free-standing assembly.
The swelling-induced delamination of thin polymer films from their deposition substrate is limited by the strain energy in the swollen film. This limitation results in a minimum thickness that can be delaminated as shown by Equation (1), a limitation which is usually circumvented by the use of sacrificial materials. In the protocol described here, no sacrificial materials are necessary because the interfacial peeling energy has been lowered by the PDAC-modification of the deposition substrate. Using this technique, we have delaminated polyvinyl formal films as thin as 8 nm, which is a factor of ten thinner than what is possible without the PDAC treatment. An ellipsometric measurement of a free-standing 8 nm film is shown in Figure 3.
<img alt="Figure 3" src="/files/ftp_upload/52832/52832fig3.jpg" /> 
Figure 3. Spectroscopic ellipsometric data on a free-standing film collected at 65&#176;, 70&#176;, and 75&#176; angles of incidence. For both &#968; and &#948;, the curves for 65&#176;, 70&#176;, and 75&#176; are arranged bottom to top. The model fits are generated using standard ellipsometric software using a Cauchy-void stack. The best-fit thickness for this film is 8.0 nm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52832/52832fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The PDAC is effective because it decreases the interfacial peeling energy between the deposition substrate and the polymer. It is not a sacrificial layer, as evidenced by XPS spectra in Figure 4 showing its presence on the deposition substrate both before and after delamination. In fact, once treated with PDAC, a substrate can be utilized to deposit and delaminate films multiple times (at least up to ten) without any noticeable change in performance. The strong binding of the PDAC to the substrate is due to the strong electrostatic interaction between the positively charged polyelectrolyte and the negatively charged silicon substrate. 22,23
<img alt="Figure 4" src="/files/ftp_upload/52832/52832fig4.jpg" /> 
Figure 4. X-ray photoelectron spectroscopy (XPS) data of wafers coated with PDAC before and after liftoff. The spectrum is largely unchanged, indicating that little if any PDAC is removed during the process. Open circles are data and the dashed lines are constituent peaks of C-N and C-C bonds. The solid black line is the enveloping curve. The reference curve is a thick (~20 nm) film of PDAC. Reprinted with permission from [14]. Copyright 2014 American Chemical Society. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52832/52832fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Despite its strong binding to the substrate, the PDAC binds only weakly to the overlying polymer thin film. The quaternary amine side chains of PDAC likely limit the interaction between the treated substrate and the polymer film to weak van der Waal&#8217;s forces, a mechanism which is applicable to a number of different polymer thin films. We have used the protocol described here to delaminate and fabricate free-standing thin films of polystsyrene (PS), polymethyl methacrylate (PMMA), and polyvinyl butyral. Recipes for preparing solutions and spin-coating parameters can be found for PS and PMMA. 24 We expect that this procedure can be generalized to other polymer systems as well, although it likely will not work for polyelectrolyte multilayers or partially acidic copolymers due to the potential for strong binding to the PDAC-treated substrate. The liftoff procedure must also be performed under pH and ionic conditions that will neither remove the PDAC from the substrate nor damage the polymer film to be delaminated.
This protocol represents a significant alternative to the use of sacrificial materials, which is the current state of the art for releasing ultrathin polymer films from their substrates. A separate optimization of the sacrificial material deposition is no longer required, and the self-limiting PDAC treatment is easily scalable to large areas as demonstrated here. We have found that films released using sacrificial underlayers display degraded strength characteristics. 14 This protocol will enable researchers to move one step closer to probing truly intrinsic mechanical properties of the free-standing polymers as well as applications in biomaterials or filtration requiring large-area thin films.

Free-standing thin polymer films are used in a variety of applications including sensors, 1-3 MEMs, catalysis or filtration, 4 and tissue engineering. 5-8 They are also used for fundamental studies exploring the behavior of polymers under confinement. 9-13 A free-standing film is one that is supported on a non-continuous substrate such as an annular ring or hoop as opposed to a silicon wafer or glass slide. This work describes a simple, repeatable fabrication procedure for ultrathin free-standing polymer films that is suitable for large-area films or high-throughput production. It is compatible with a variety of different polymers, including poly(vinyl formal), polystyrene, and poly(methyl methacrylate). It can be used to fabricate free-standing films that are as large as 13-cm diameter or as thin as 10 nm.
The fabrication of free-standing polymers consists of three basic steps: 1) deposition of polymer film onto a traditional substrate such as a wafer or slide, 2) release or liftoff of the film from the substrate, and 3) capture of the resultant film onto a support. This paper details a procedure that we reported in an earlier study on various release methods. 14
Deposition can be achieved by any number of basic polymer thin film technologies such as spin-coating, vapor deposition, or dip-coating. In this work, we utilize standard spin-coating techniques.
The &#8220;lift off-float on&#8221; technique is the most common method for releasing an ultrathin film from its substrate. 15 In this technique, the film and substrate are immersed in a suitable solvent bath. The solvent swells the film and induces spontaneous delamination, releasing the film and allowing it to float to the top of the bath. The minimum film thickness that can be released using lift off-float on is determined by balancing the interfacial peeling energy with the swelling-induced strain energy: 16
<img alt="Equation 1" src="/files/ftp_upload/52832/52832eq1.jpg" width="200" />&#160;&#160;&#160;&#160;&#160;(1)
Where L is the film thickness, &#957;f is the Poisson&#8217;s ratio of the film, E is the Young&#8217;s modulus of the film, &#958; is the swelling ratio of the film, and &#947; is the interfacial energy of peeling. The typical way to bypass the limitation imposed by Equation (1) is to deposit a sacrificial interlayer between the film and the deposition substrate. 17-20 When this interlayer dissolves in a solvent bath, the film is released and can be captured on a support. A related method is the sacrificial overlayer method, which utilizes mechanical peeling of the film onto a sacrificial layer prior to dissolution. 21
The use of sacrificial materials has several chief drawbacks. First, the addition of an extra process material and step may require a compromise between optimal film fabrication conditions and sacrificial material processing conditions. Second, sacrificial materials may be difficult to deposit without affecting the mechanical properties or purity of the final free-standing film. Third, the process for depositing the sacrificial material must be optimized and monitored for quality as an operation in the overall free-standing film fabrication. 14
In this work, we describe a surface modification technique that decreases the interfacial peeling energy, enabling the lift off-float on technique to be used for ultrathin films. The deposition substrate is modified by assembling a self-limited, self-optimizing near-monolayer of the polycation polydiallyldiammonium chloride (PDAC). Because of the strength of the binding between the polycation and the substrate, this surface modification is robust to subsequent process steps. The self-limiting and self-optimizing nature of the near-monolayer formation requires practically zero optimization and is easily scalable to large areas.
Following removal, the film floats to the top of the solvent bath where it is captured on a hoop-like support. While not given much attention in the extant literature, in this work we will describe techniques for capturing large-area films on supports that reduce the probability of tearing or otherwise damaging the film.

<table><tbody><tr><td>Vinylec E</td><td>SPI</td><td></td><td></td></tr><tr><td>ethyl lactate, &gt;98%, FCC, FG</td><td>Sigma-Aldrich</td><td>W244007-1KG-K</td><td></td></tr><tr><td>4&quot; silicon wafers &amp;lt;100&gt;, Single side polished</td><td>International Wafer Service</td><td></td><td></td></tr><tr><td>sulfuric acid, 98%, ACS reagent grade</td><td>Sigma-Aldrich</td><td>320501-6X500ML</td><td></td></tr><tr><td>hydrogen peroxide, 30%, semiconductor grade</td><td>Sigma-Aldrich</td><td>316989-3.7L</td><td></td></tr><tr><td>isopropanol, ACS grade, 4 L</td><td>Fisher Scientific</td><td>A464-4</td><td></td></tr><tr><td>dichloromethane, ACS grade</td><td>Alfa-Aesar</td><td>22917</td><td></td></tr><tr><td>deionized water, distilled</td><td></td><td></td><td></td></tr><tr><td>PDAC reagent (Sigma-Aldrich 409014)</td><td>Sigma-Aldrich</td><td>409014</td><td></td></tr><tr><td>Spin Coater</td><td>Laurell Technologies&amp;nbsp;</td><td>WS-650-23</td><td></td></tr><tr><td>Barnstead/Thermolyne Super Nuova explosion-proof hot plate&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>explosion-proof forced air oven</td><td>VWR&amp;nbsp;</td><td>1330 FMS&amp;nbsp;</td><td></td></tr><tr><td>balance with a range of 1&amp;nbsp;mg to 1,020&amp;nbsp;g</td><td>Mettler Toledo</td><td>MS1003S</td><td></td></tr><tr><td>reflectance spectrometer</td><td>Filmetrics</td><td>F20-UV</td><td></td></tr><tr><td>manipulator consisting of a Klinger tilt stage, a Brinkman rack-and-pinion and a lab jack&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Cutting tool/template, LLNL-built, no drawings</td><td></td><td></td><td></td></tr><tr><td>straight edge, LLNL, no drawings</td><td></td><td></td><td></td></tr><tr><td>Tent hoop, LLNL</td><td></td><td></td><td></td></tr><tr><td>culture dish 190 mm x 100 mm, Pyrex</td><td>VWR</td><td></td><td></td></tr><tr><td>20 ml beaker, Pyrex</td><td>VWR</td><td></td><td></td></tr><tr><td>250 ml beaker, Pyrex</td><td>VWR</td><td></td><td></td></tr><tr><td>1,000 ml beaker, Pyrex</td><td>VWR</td><td></td><td></td></tr><tr><td>60 ml glass vial with plastic stopper&amp;nbsp;</td><td>VWR</td><td></td><td></td></tr><tr><td>Petri dish, 150 mm diameter x2, Pyrex</td><td>VWR</td><td></td><td></td></tr><tr><td>600 ml beaker x2, Pyrex</td><td>VWR</td><td></td><td></td></tr><tr><td>tweezers, stainless steel</td><td></td><td></td><td></td></tr><tr><td>cutting blade</td><td>Exacto</td><td></td><td></td></tr><tr><td>clean room wipes</td><td>Contec&amp;nbsp;</td><td>PNHS-99</td><td></td></tr><tr><td>polyester knit 9/91 IPA/DI water wipes</td><td>Contec&amp;nbsp;</td><td>Prosat&amp;nbsp;</td><td></td></tr><tr><td>Fluoroware wafer trays</td><td>Ted Pella</td><td>1395-40</td><td></td></tr><tr><td>Nylon Micro fiber (camel hair)</td><td></td><td></td><td></td></tr><tr><td>Disposable BD 3-ml plastic syringe</td><td>VWR</td><td></td><td></td></tr><tr><td>0.2 &amp;#956;m Luer-lock PTFE filters</td><td>Acrodisc&amp;nbsp;</td><td></td><td></td></tr><tr><td>0.45 &amp;#956;m Luer-lock PTFE filters</td><td>Acrodisc&amp;nbsp;</td><td></td><td></td></tr></tbody></table>

fabrication of large-area free-standing ultrathin polymer films

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described.

Figure 1 shows an example of a free-standing thin polymer film over a large area. This 55 nm thick polyvinyl formal film was fabricated using the procedure described here and is mounted on a 13-cm diameter steel hoop. The delamination occurs over large areas without introducing defects that lead to tearing of the film. Thus, the intrinsic strength of polyvinylformal can be exploited even for very thin films. Figure 2 shows a 22 nm thick free-standing film that is strong enough to be loaded with a watch glass and copper beads that weigh &#62;3x105 times the mass of the film itself. Spectroscopic ellipsometry can be used to confirm the thickness of the freestanding film. Figure 3 shows ellipsometric data for an 8.0 nm film. Silicon surfaces treated with PDAC can be used multiple times for film delamination; X-ray photoelectron spectroscopy (XPS) spectra in Figure 4 show that once deposited, the PDAC is robustly attached to the surface and is not removed during the lift-off procedure.
<img alt="Figure 1" src="/files/ftp_upload/52832/52832fig1.jpg" /> 
Figure 1. A 55 nm thick polyvinyl formal film mounted on a 13 cm diameter steel hoop. Reprinted with permission from [14]. Copyright 2014 American Chemical Society. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52832/52832fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/52832/52832fig2.jpg" /> 
Figure 2. A 22 nm thick, 13 cm diameter polyvinyl formal film loaded with a watch glass and copper beads. The total mass supported by the film is 10.5 g, while the mass of the film is estimated to be 0.336 mg. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52832/52832fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Fabrication of Large-area Free-standing Ultrathin Polymer Films at JoVE.com

Fabrication of Large-area Free-standing Ultrathin Polymer Films

We describe a method for the fabrication of large-area (up to 13 cm diameter) and ultrathin (as thin as 8 nm) polymer films. Instead of using a sacrificial interlayer to delaminate the film from its substrate, we use a self-limiting surface treatment suitable for arbitrarily large areas.

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films.  Typically, ultrathin films are prepared ...

fabrication-of-large-area-free-standing-ultrathin-polymer-films

Nanyang Technological University

Research

JoVE Journal

Chemistry

15.3K Views.  Lawrence Livermore National Laboratory. We describe a method for the fabrication of large-area (up to 13 cm diameter) and ultrathin (as thin as 8 nm) polymer films. Instead of using a sacrificial interlayer to delaminate the film from its substrate, we use a self-limiting surface treatment suitable for arbitrarily large areas.

Video: Fabrication of Large-area Free-standing Ultrathin Polymer Films

Micropunching Lithography for Generating Micro- and Submicron-patterns on Polymer Substrates

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of low weight, easy tailoring of properties and a wide spectrum of applications2,3. Due to sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature and chemical solutions), lithographic techniques present significant technical challenges when working with these materials4. For example, current photolithographic methods, such as ultra-violet (UV), are unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in these methods. In addition, current micro/nanosystems mainly have a planar form5,6. One layer of structures is built on the top surfaces of another layer of fabricated features. Multiple layers of these structures are stacked together to form numerous devices on a common substrate. The sidewall surfaces of the microstructures have not been used in constructing devices. On the other hand, sidewall patterns could be used, for example, to build 3-D circuits, modify fluidic channels and direct horizontal growth of nanowires and nanotubes.
A macropunching method has been applied in the manufacturing industry to create macropatterns in a sheet metal for over a hundred years. Motivated by this approach, we have developed a micropunching lithography method (MPL) to overcome the obstacles of patterning conducting polymers and generating sidewall patterns. Like the macropunching method, the MPL also includes two operations (Fig. 1): (i) cutting; and (ii) drawing. The "cutting" operation was applied to pattern three conducting polymers4, polypyrrole (PPy), Poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT) and polyaniline (PANI). It was also employed to create Al microstructures7. The fabricated microstructures of conducting polymers have been used as humidity8, chemical8, and glucose sensors9. Combined microstructures of Al and conducting polymers have been employed to fabricate capacitors and various heterojunctions9,10,11. The "cutting" operation was also applied to generate submicron-patterns, such as 100- and 500-nm-wide PPy lines as well as 100-nm-wide Au wires. The "drawing" operation was employed for two applications: (i) produce Au sidewall patterns on high density polyethylene (HDPE) channels which could be used for building 3D microsystems12,13,14, and (ii) fabricate polydimethylsiloxane (PDMS) micropillars on HDPE substrates to increase the contact angle of the channel15.

A micropunching lithography approach is developed to generate micro- and submicron-patterns on top, sidewall and bottom surfaces of polymer substrates. It overcomes the obstacles of patterning conducting polymers and generating sidewall patterns. This method allows rapid fabrication of multiple features and is free of aggressive chemistry.

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of ...

Engineering

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application.
Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients.
The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

In this paper we describe the interfacial synthesis of conjugated microporous polymers (CMP) on sacrificial substrates, and the dissolution of the substrate for the preparation of freestanding CMP nanomembranes. In addition, we will describe how the fragile nanomembranes can be transferred to other substrates.

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in ...

Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. Conductive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT), and a semiconducting polymer, poly(thieno[3,2-b]thiophene) (PTT), were deposited on unconventional highly-disordered and textured substrates with high surface areas, such as paper, towels and fabrics. This reported deposition chamber is an improvement of previous vapor reactors because our system can accommodate both volatile and nonvolatile monomers, such as 3,4-propylenedioxythiophene and thieno[3,2-b]thiophene. Utilization of both solid and liquid oxidants are also demonstrated. One limitation of this method is that it lacks sophisticated in situ thickness monitors. Polymer coatings made by the commonly used solution-based coating methods, such as spin-coating and surface grafting, are often not uniform or susceptible to mechanical degradation. This reported vapor phase deposition method overcomes those drawbacks and is a strong alternative to common solution-based coating methods. Notably, polymer films coated by the reported method are uniform and conformal on rough surfaces, even at a micrometer scale. This feature allows for future application of vapor deposited polymers in electronics devices on flexible and highly textured substrates.

This paper presents a protocol for reactive vapor deposition of poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), and poly(thieno[3,2-b]thiophene) films on glass slides and rough substrates, such as textiles and paper.

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Fabricating Reactive Surfaces with Brush-like and Crosslinked Films of Azlactone-Functionalized Block Co-Polymers

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl dimethyl azlactone) (PGMA-b-PVDMA), are presented. Due to the high reactivity of azlactone groups towards amine, thiol, and hydroxyl groups, PGMA-b-PVDMA surfaces can be modified with secondary molecules to create chemically or biologically functionalized interfaces for a variety of applications. Previous reports of patterned PGMA-b-PVDMA interfaces have used traditional top-down patterning techniques that generate non-uniform films and poorly controlled background chemistries. Here, we describe customized patterning techniques that enable precise deposition of highly uniform PGMA-b-PVDMA films in backgrounds that are chemically inert or that have biomolecule-repellent properties. Importantly, these methods are designed to deposit PGMA-b-PVDMA films in a manner that completely preserves azlactone functionality through each processing step. Patterned films show well-controlled thicknesses that correspond to polymer brushes (~90 nm) or to highly crosslinked structures (~1-10 &#956;m). Brush patterns are generated using either the parylene lift-off or interface directed assembly methods described and are useful for precise modulation of overall chemical surface reactivity by adjusting either the PGMA-b-PVDMA pattern density or the length of the VDMA block. In contrast, the thick, crosslinked PGMA-b-PVDMA patterns are obtained using a customized micro-contact printing technique and offer the benefit of higher loading or capture of secondary material due to higher surface area to volume ratios. Detailed experimental steps, critical film characterizations, and trouble-shooting guides for each fabrication method are discussed.

Surface fabrication methods for patterned deposition of nanometer thick brushes or micron thick, crosslinked films of an azlactone block co-polymer are reported. Critical experimental steps, representative results, and limitations of each method are discussed. These methods are useful for creating functional interfaces with tailored physical features and tunable surface reactivity.

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl ...

Thin Film Composite Silicon Elastomers for Cell Culture and Skin Applications: Manufacturing and Characterization

In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin adhesives. Two different poly-(dimethyl siloxanes) (PDMS and soft skin adhesive (SSA)), have been used for in depth investigation of biological effects and adhesive characteristics. The composite films consist of a flexible backing layer and an adhesive top coating. Both layers have been manufactured by doctor blade application technique. In the present investigation, the adhesive behavior of the composite films has been investigated as a function of the layer thickness or a variation of the Young&#39;s modulus of the top layer. The Young&#39;s modulus of PDMS has been changed by varying the base to crosslinker mixing ratio. In addition, the thickness of SSA films has been varied from approx. 16 &#181;m to approx. 320 &#181;m. Scanning electron microscopy (SEM) and optical microscopy have been used for thickness measurements. The adhesive properties of elastomer films depend strongly on the film thickness, the Young&#39;s modulus of the polymers and surface characteristics. Therefore, normal adhesion of these films on glass substrates exhibiting smooth and rough surfaces has been investigated. Pull-off stress and work of separation are dependent on the mixing ratio of silicone elastomers.
Additionally, the thickness of the soft skin adhesive placed on top of a supportive backing layer has been varied in order to produce patches for skin applications. Cytotoxicity, proliferation and cellular adhesion of L929 murine fibroblasts on PDMS films (mixing ratio 10:1) and SSA films (mixing ratio 50:50) have been conducted. We have shown here, for the first time, the side by side comparison of thin composite films manufactured of both polymers and present the investigation of their biological- and adhesive properties.

A protocol for the manufacturing process of polymeric thin film composite structures possessing either different Young&#39;s moduli or thicknesses is presented. Films are produced for advanced cell culture studies or as skin adhesives.

In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin ...

Developmental Biology

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support ...

A Femtoliter Droplet Array for Massively Parallel Protein Synthesis from Single DNA Molecules

Advances in spatial resolution and detection sensitivity of scientific instrumentation make it possible to apply small reactors for biological and chemical research. To meet the demand for high-performance microreactors, we developed a femtoliter droplet array (FemDA) device and exemplified its application in massively parallel cell-free protein synthesis (CFPS) reactions. Over one million uniform droplets were readily generated within a finger-sized area using a two-step oil-sealing protocol. Every droplet was anchored in a femtoliter microchamber composed of a hydrophilic bottom and a hydrophobic sidewall. The hybrid hydrophilic-in-hydrophobic structure and the dedicated sealing oils and surfactants are crucial for stably retaining the femtoliter aqueous solution in the femtoliter space without evaporation loss. The femtoliter configuration and the simple structure of the FemDA device allowed minimal reagent consumption. The uniform dimension of the droplet reactors made large-scale quantitative and time-course measurements convincing and reliable. The FemDA technology correlated the protein yield of the CFPS reaction with the number of DNA molecules in each droplet. We streamlined the procedures about the microfabrication of the device, the formation of the femtoliter droplets, and the acquisition and analysis of the microscopic image data. The detailed protocol with the optimized low running cost makes the FemDA technology accessible to everyone who has standard cleanroom facilities and a conventional fluorescence microscope in their own place.

The overall goal of the protocol is to prepare over one million ordered, uniform, stable, and biocompatible femtoliter droplets on a 1 cm2 planar substrate that can be used for cell-free protein synthesis.

Advances in spatial resolution and detection sensitivity of scientific instrumentation make it possible to apply small reactors for biological and ...

A Simple and Scalable Fabrication Method for Organic Electronic Devices on Textiles

Today, wearable electronics devices combine a large variety of functional, stretchable, and flexible technologies. However, in many cases, these devices cannot be worn under everyday conditions. Therefore, textiles are commonly considered the best substrate to accommodate electronic devices in wearable use. In this paper, we describe how to selectively pattern organic electroactive materials on textiles from a solution in an easy and scalable manner. This versatile deposition technique enables the fabrication of wearable organic electronic devices on clothes.

In this paper, we present a protocol to selectively deposit organic materials on textiles, which allows for the direct integration of organic electronic devices with wearables. The fabricated devices can be fully integrated in textiles, respecting their mechanical appearance and enabling sensing capabilities.

Today, wearable electronics devices combine a large variety of functional, stretchable, and flexible technologies. However, in many cases, these devices ...

Fabrication of Large-area Free-standing Ultrathin Polymer Films

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